1. Field of the Invention
The present invention relates to exposure techniques and in particular to an apparatus for correcting a plurality of exposure tools, a method for correcting a plurality of exposure tools, and a method for manufacturing semiconductor device.
2. Description of the Related Art
As semiconductor devices continue to shrink in size over time, so do the individual circuit patterns. Therefore, reproducing a designed circuit pattern on a wafer by exposing a reticle has recently become difficult. There are many types of exposure tools used in lithography processes. Especially, an exposure tool employing reduction step-and-scan method is one of the representatives. However, since a numerical aperture affects the depth of focus (DOF), problems arise. For example, increasing the numerical aperture imposes restrictions on the resist film thickness. Also, an aberration imposes restrictions on an area of an exposure field.
In Japanese Patent No. 2634037, modifying the shape of a light source in the exposure tool is proposed to solve the problem of decreased DOF. Also, in Japanese Patent Laid-Open Publication No. 2001-144009, tilting a wafer stage in the exposure tool is proposed to solve such problem. However, even though lithography techniques for correcting an individual exposure tool exist, a method for correcting an ununiformity of a plurality of the exposure tools has not been existed.
For example, line width foreshortening is typically observed in the lithography processes. The line width foreshortening depends on a pitch of transparent patterns delineated in the reticle. Such phenomena are called optical proximity effect (OPE). Optical proximity effects of the plurality of the exposure tools are different from each other. Therefore, even though an identical reticle is used for the lithography processes, the line width of the projected patterns varies dependent on the exposure tools. Consequently, uniformity of manufactured semiconductor devices is decreased. Therefore, each reticle should have been modified to adapt to individual OPE of the exposure tool. When semiconductor devices are manufactured by the plurality of the exposure tools, preparing a plurality of the reticles is required, which increases a manufacturing cost of the semiconductor device.